This invention relates to a robot wrist and to a robot provided with a robot wrist. In particular, the invention is concerned with a robot wrist having a high orientation capacity, .theta.. (In this connection the term "orientation capacity" refers to that ratio of the surface area of a sphere of given radius, centered on the point of articulation of the wrist, to the surface area of the spherical or part spherical surface of the same radius which can be reached by a member articulated by the wrist. Thus the orientation capacity .theta. ranges from 0 to 1, a high value for .theta., e.g. .theta.=0.8, indicating that the wrist has a high degree of orientation about its point of articulation).
For operations such as arc welding, glueing, puttying, burring, and so on, involving the use of industrial robots operable within confined spaces, e.g., inside box-shaped objects such as the insides of car bodies, heavy demands are placed on the industrial robots used. In order to perform such operations the robot should have at least six axes of movement to enable a tool carried by the robot to be positioned, aligned and adjusted at any desired location within its operating range. Three such axes are normally provided in the robot itself and the other three axes provided in the robot wrist.
The robot arm and the robot wrist should also be hollow to accommodate a channel for cables and other wires in the robot arm and robot wrist. This channel should have a large radius of curvature and be otherwise so shaped as not to damage the cables and wire during operation of the robot, for example when the robot has a bent wrist.
To move a tool or a welding tip with a constant angle towards a working surface in a box, an orientation capacity of .theta.=0.8 is required. This means that the wrist should be capable of being deflected at least 135.degree. from the central axis of the robot arm carrying the wrist and be capable of adopting any angular position around the central axis of the robot arm.
The present invention aims to provide a robot wrist with a large orientation capacity and with three axes of movement.
A further aim of the invention is to provide a channel through the wrist for the passage of wires, cables or conduits for operating a tool carried by the wrist.